This invention relates generally to a gear train of the type used in an analog timepiece and more particularly to a gear train mechanism wherein wheels in the train between the motor rotor and the second hand are substantially overlapped and the number of wheels in said train is reduced over the conventionally used gear trains.
In recent years, with progress in the electronic arts, the elements of a timepiece have been made small in size and thin, and as a result, it has been possible to produce thin electric timepieces. However, the face of the electric timepiece remained large, or when the timepieces were small in size, they were not provided with a second hand. On the other hand, during the same years, market demand from users has been continuously directed to the design of a timepiece which is small in face size, thin and yet provides for performance of multifunctions such as provision of a second hand.
In order to provide a small-sized timepiece, the parts of the timepiece, for example, the battery, coil, gear train, etc., must be made as small as possible and must also be arranged as close as possible to the center of the timepiece. Generally speaking, when making a small and thin timepiece, the outer diameter of a timepiece having three hands, namely, a second, minute and hour hand, is defined by the outer diameter of the battery and the radius of the wheel for driving the second hand, that is, the fourth wheel. As the dimensions of a battery greatly influence its capacity for power delivery, and in view of the relationship between current consumption and battery life, there is a practical limit to any reductions in size which may be made in battery design.
At the present time, taking as an example a threehanded timepiece with a battery life of nearly two years, a battery with an outer diameter of 7.9 millimeters and a thickness of 2.7 millimeters is the smallest which can be used. Applying this battery in a timepiece having an outer diameter of about 18 millimeters, the diameter of the wheel for driving the second hand must be about 2 millimeters. This is a small and often inconvenient dimension for mass-production methods.
What is needed is a gear train mechanism for a timepiece which is compact and provides a highly reliable timepiece of small dimensions and having reduced mechanical complexity.